If, in the end, Russian air strikes in Syria are subjected to an American veto, the Assad regime is kept from striking civilian neighborhoods, and significant aid flows resume to opposition areas, something of great value will have been accomplished. Nothing good can happen politically in Syria unless civilians are removed from the Assad regime and Russian bullseye. Nothing. If this agreement can spare Syrian civilians from continued mass murder it will be good in and of itself. There are however good reasons to believe the gains will be limited or temporary, judging from the regime’s track record during the previous cessation of hostilities and the lack of any enforcement mechanism.

Separating Nusra Front fighters from mainstream rebels will be very difficult however. The Russian-regime decision several weeks back to try to surround and besiege Aleppo led all anti-Assad regime forces in the area to coalesce to resist. They had some success. Now that the siege is again being imposed, how are those resisting to be separated? Even if opposition forces wished it, they could not conceivably confront the Nusra Front anyway. Meanwhile, they would be accused of harboring or cooperating with jihadists, and many including US-allied groups may therefore be targeted, which may further radicalize the support base and fighters of the Syrian opposition. Arguably, even if the deal weakens the Nusra Front, if it is not paired with increased support for alternative opposition groups this simply positions the regime to resume the war further down the line on more advantageous terms.

Indeed, a major near-term challenge is that neither the Nusra Front nor the Assad regime (nor ISIS, for that matter) is strongly motivated to cooperate with a new cessation of hostilities. When the original Cessation of Hostilities worked for a few weeks back in February and March, civilians all across northern Syria rose up peacefully against both the Assad regime and the Nusra Front: both use violence and terror to subject civilians and both profit enormously from ongoing violence. If regime airstrikes on civilian neighborhoods are pared back, will Assad's army and Iranian-organized militias - who are apparently not mentioned in the new deal at all - also refrain from artillery and mortar strikes?

Kerry and Lavrov are right: there are many chefs in the kitchen and there will have to be cooperation for all of this to work. Unfortunately the question of regime detainees—tens of thousands—seems not to have been addressed, nor that of freedom of movement or lifting of sieges. And with the siege of Aleppo being reinstated it's quite possible that the Russians have achieved their goal of making Assad immune to a negotiated removal. Indeed, the highly-contested Ramouseh area in southwest Aleppo, where the Nusra Front and other hardline groups temporarily broke the regime siege of Aleppo, is apparently excluded from this latest deal altogether. If this intends to allow for looser targeting and rules of engagement, then a US-Russian deal is being reached to eliminate the armed opposition from this area.

Still: nothing good in Syria is possible until the wholesale slaughter of civilians stops and humanitarian assistance flows freely in accordance with multiple UN Security Council resolutions. If John Kerry can pull this off he deserves a great deal of credit. But it will require the Russians, the Iranians, and their Syrian client to act in unnatural ways reflecting decency and respect for human life, and arguably undermining some of their more successful military tactics including siege and bombing population zones. It's still a long shot.

Frederic C. Hofis director of the Atlantic Council's Rafik Hariri Center for the Middle East. Faysal Itani is a senior fellow with the Atlantic Council’s Rafik Hariri Center for the Middle East.